The present invention relates to a hub for a helicopter rotor which can support a plurality of blades connectable to the hub itself by means of associated elastomeric couplings.
In helicopter rotors it is known to utilize hubs constituted by a flat plate having in plan a substantially regular polygonal from the number of sides of which, normally four, is equal to the number of blades to be supported. The said flat plate is normally constituted by a single plate of metal material or else of laminated synthetic material which is provided, near each of its corners, with a through hole which is closed on the outside by a peripheral arm or bridge. Each blade is normally provided with an attachment bracket which extends through an associated through hole of the said plate and is supported by the associated bridge with the interposition of a resilient block, normally of frustoconical form, disposed with its axis coplanar to the said plate and directed towards an axis of rotation of the rotor.
From what has been described above it is apparent that all the forces transmitted from the hub to the blade and all the forces applied by the blades to the hub pass through the said peripheral arms or bridges the points of connection of which with the remaining parts of the hub are certainly the most stressed points of the hub itself. In particular, the concentration of forces which occurs at the ends of the said bridges is normally such as to require relatively great thicknesses of material for their absorption.
A first disadvantage of the known hubs described above is constituted by the fact that the material used is, in general, only just sufficient at the points of greatest force concentration and certainly stronger than is required at all other points. This means, obviously, a reduction in the "payload" for an installation of the same power.
A further disadvantage of the known hubs described above lies in the fact that the substantially monolithic structure of the hubs themselves favours the propagation of possible cracks.